It is not easy to allocate bands as wide as a bandwidth for TV signals with respect to digital video signals which are transmitted and received by a mobile phone and a notebook, which are prevalently in use, a mobile television and a handheld PC which will be used prevalently in future. Hence, standard of video compression for mobile devices should provide higher video signal compression efficiency.
Moreover, such mobile devices inevitably have varying inherent capabilities of processing or presenting video signals. Therefore, a compressed image must be variously prepared in advance to correspond to such capabilities, which means that video data having various image qualities, with respect to various combined parameters, such as the number of frames per second, the resolution, and the number of bits per pixel, must be provided for a single image source, thus inevitably placing a great burden on content providers.
On this account, the content providers prepare compressed video data having a high bit rate for each individual image source, and, when the mobile device requests the video data, perform a procedure of decoding a compressed image and encoding the decoded image into video data suitable for the video processing capability of the mobile device that requested the image, and then provides the encoded video data. In doing so, since the transcoding, which implies the decoding and the encoding, is requisite, a time delay occurs until providing the video data requested by the mobile device. Also, the transcoding requires complicated hardware devices and algorithms depending on the variety of encoding targets.
A scalable video codec (SVC) is suggested as a solution for the above disadvantages. The SVC encodes a video signal at maximum quality and allows the video presentation of low quality even when a partial sequence, which is a sequence of a frame selected intermittently from the entire sequence, of the generated picture sequence produced from the encoding. A motion compensated temporal filter (MCTF) scheme is the encoding scheme suggested for the SVC.
As discussed above, while the picture sequence encoded in the scalable MCTF can present the video of low quality merely by receiving and processing the partial sequence, the image quality degrades considerably when the bit rate lowers. To overcome this disadvantage, an auxiliary picture sequence for low transmission rate, for example, a picture sequence having small screen and/or low frames per second may be provided separately. The auxiliary sequence is referred to as a base layer, and the main picture sequence is referred to as an enhanced or enhancement layer. But, since the base layer and the enhanced layer encode the same video signal source, redundant information (redundancy) is present in the video signal in both layers.
To improve the coding efficiency of the enhanced layer encoded according to the MCTF scheme, a prediction image of the enhanced layer is generated from an arbitrary video frame of the base layer temporally coincident with the video frame of the enhanced layer, as shown in FIG. 1.
Referring to FIG. 1, a certain number of macro blocks of the base layer are reconstructed as one picture, and the picture is enlarged to the size equal to the video frame of the enhanced layer by up-sampling the picture (S10). When the macro block BM10, in the enlarged picture B100, at the same position as the macro block EM10 in the frame E100, which is temporally coincident with the enlarged picture B100 of the base layer, of the enhanced layer of which the current prediction image is to be generated, is coded as an intra mode, a prediction procedure for the macro block EM10 of the enhanced layer is carried out based on the macro block BM10 (S11).
In more detail, after the original block image of the macro block BM10, coded in a intra mode, of the base layer is recovered using pixel values of lines adjacent to the macro block BM10, a difference or error value of the recovered block image, that is, residual is encoded to the macro block EM10 of the enhanced layer. The coded macro block EM10 is referred to as an intra BL mode.
The scheme using the original image of the intra mode block of the base layer needs to recover first the original image of the intra mode block of the base layer which is to be used for encoding and decoding image blocks in the arbitrary frame of the enhanced layer, according to the prediction information. The problem is that this recovery requires pretty high hardware complexity.